External engine balance - how's it done?

[Moparmal]

Im interested in knowing exactly what an engine builder does when they externally balance a 360 rotating assembly.

Lets assume we're using the B&M flex plate, Neutral converter and a 360 Dampner.......What else is involved in the process?

 

[fishy68]

I'm no guru on this subject but I'll share what I know. The process is the same for internally or externally balancing. The only difference is an externally balanced engine has weight added to the balancer and flywheel/torque converter 180 degrees opposite each other to balance the engine because the crank doesn't weigh enough to balance it internally.

BTW: This added weight out on the end of the crank opposite each other adds stress to the crank so that's why an internally balanced engine is better. You can internally balance any crank but that involves adding Mallory metal (very heavy metal) in various places on the crank and Mallory metal is very expensive.

To balance an engine they weigh the pistons then the heavy ones get material removed to match the weight of the lightest piston. Same goes for the rods. Then they figure up the bob weight (sorry, don't know that formula) and add the bob weights to the rod journals and spin it and remove weight where needed to balance it out.

 

[dgc333]

The process is the same. The external balanced damper and flywheel/flexplate/troque convertor must be on the ends of the crank when it's done. They will still add or remove metal from the counter weights at the ends of the crank to obtain the balance.

 

[Tony Fields]

Here's what it looks like....360 stuff



Setting up the bob weights

Heavy metal was added to the crank during this process

Atttached the neutral convertor to see how good it was

Here are the final numbers on the balance with the convertor
bolted on

I'm not sure what all this means.....I just took the pick's to document
my engine build for my restoration book.

 

[754door]

You take the reciproctaing weight which is piston, pin, rings, and small end of rod add them together. then you have reciprocating weight. then rotating weight is the big end of rod and bearings you get that number and times it by 2 because that is the number of rods per throw. Then you add in your oil weight which is about 3 to 5gm. then you have your bobweight. The formula is 100% rotating and 50% recip. That is for a v-8. Also I should at that most 60degree v-6s and 90degree v-6 with two rods per journal use the same formula.